1. Field of Invention
The present invention relates generally to network systems. More particularly, the present invention relates to enabling path protected circuits to be created within open ended unidirectional path protected switched rings that have nodes which are associated with multiple vendor or service provider equipment networks.
2. Description of the Related Art
The demand for data communication services is growing at an explosive rate. Much of the increased demand is due to the fact that more residential and business computer users are becoming connected to the Internet. Furthermore, the types of traffic being carried by the Internet are shifting from lower bandwidth applications towards high bandwidth applications which include voice traffic and video traffic.
To address the demand for data communication services, the use of optical networks, such as a synchronous optical network (SONET), is becoming more prevalent. A SONET network is an example of a time division multiplexed (TDM) network. TDM networks generally allocate single lines to be used amongst multiple users, or customers of data communication services. The single lines may each be divided into slots of time during which each user has access to the single lines.
A network such as a TDM network is generally designed to ensure that information may be transferred between nodes within the network. Often, within a network, information is transferred between two specified nodes, i.e., a source node which sends information and a destination node which receives information. When information is to be sent between a source node and a destination node, a circuit path between the two nodes must be computed so that leased line services may be provided.
In order to increase the likelihood that data will be successfully transferred between a source node and a destination node, a circuit path between the source node and the destination node may be protected. A protected circuit path is a circuit path which includes redundancy that generally allows data to be transferred even in the event of a nodal failure or a link failure. A protected path may generally include protected links, e.g., links with 1+1 protection, and unprotected links. When unprotected links are included in a protected circuit path, an alternate circuit path is associated with the protected circuit path. If a primary circuit path between a source node and a destination node includes unprotected links, then an alternate circuit path is needed between the source node and the destination node in order for the circuit path between the source node and the destination node to be protected. The alternate circuit path effectively serves as a “back up” to a primary circuit path which includes unprotected links in the event that the primary circuit path fails. By way of example, when a primary circuit path suffers either a nodal failure or a failure of a link, information which was to be sent from a source node to a destination node on the primary circuit path may instead be sent from the source node to the destination node on the alternate circuit path.
Many networks include source nodes and destination nodes that are a part of a uni-directional path protected switched ring (UPSR). FIG. 1 is a diagrammatic representation of a UPSR. A UPSR 10 includes a multiplicity of nodes 20a-d which are communicably connected by unprotected links 22a-d. Specifically, nodes 20a, 20b are linked by link 22a, nodes 20b, 20c are linked by link 22b, nodes 20c, 20d are linked by link 22c, and nodes 20d, 20a are linked by link 22d. 
When node 20a is a source node and node 20c is a destination node, then information may be sent from source node 20a to destination node 20c on a circuit path. When the circuit path on which the information is to be sent is to be a protected circuit path, since links 22a-d are unprotected links, both a primary circuit path 24 and an alternate circuit path 26 between source node 20a and destination node 20c are needed. Alternate circuit path 26 essentially protects primary circuit path 24, since alternate circuit path 26 may be used to transmit or otherwise provide information from source node 20a to destination node 20c if there is a failure associated with primary circuit path 24.
Primary circuit path 24 includes link 22a which is effectively a segment between source node 20a and node 20b. Source node 20b may be considered to be a segment destination node for the segment which includes link 22a. Link 22b, which is effectively a segment between node 20b and destination node 20c, is also included in primary circuit path 24. Alternate circuit path 24 includes links 22d, 22c and passes through node 20d. 
Often, nodes 20a-d may be from different vendor equipment networks, e.g., at least one of nodes 20a-d may be of a different type or owned by a different service provider from other nodes 20a-d. For example, destination node 20c may be different from nodes 20a, 20b, 20d in that destination node 20c may be of a different type, or owned by a different service provider, than nodes 20a, 20b, 20d which may be of the same type, or owned by a common service provider. When destination node 20c is different from nodes 20a, 20b, 20d, primary circuit path 24 and alternate circuit path 26 are “stitched together” which involves a highly laborious process that includes going to each appropriate node 20a-d in each circuit path 24, 26 and trying to create an individual connection. Once individual connections are created, as for example by a service provider, then a set of connections is pieced together to form circuit paths 24, 26. Network management systems that are used to create circuit paths 24, 26 may generally only compute circuit paths 24, 26 to one end point, e.g., node 20c, when substantially all elements associated with UPSR 10 or, more generally, the network are known.
Creating circuit paths 24, 26 by stitching together connections is difficult, time-consuming and often inaccurate, or otherwise prone to errors. Since the speed with which circuit paths 24, 26 may be created and the transmission of information or data on appropriate paths is typically critical, the time associated with stitching together circuit paths 24, 26 and the propensity of errors associated with stitching together circuit paths 24, 26 may be unacceptable in many cases.
Therefore, what is needed is a method and an apparatus for enabling protected circuit paths to be efficiently and accurately created across multiple vendor or multiple service provider equipment networks. That is, what is desired is a system which allows path protected circuit to be substantially automatically computed within a multiple vendor or multiple service provider equipment network.